1. Field of the Invention
The present invention relates to variable flow control valves, and in particular to variable flow control valves for controlling flow of gaseous fluids, e.g., air.
2. Description of the Related Art
Japanese Laid-Open Patent Publication No. 7-279696 teaches a known throttle valve, in which resilient seal members are attached to an outer peripheral portion of a throttle valve in positions opposing to flat seat surfaces defined in an inner wall of an air flow channel of a throttle body. More specifically, the seat surfaces are defined by semi-circular arc shaped ledges formed on the inner wall of the air flow channel. The resilient seal members are made of rubber and have projections that may contact the respective ledges of the air flow channel when the throttle valve is in a close position. The projections of the seal members may be pressed against the corresponding ledges of the air flow channel due to the pressure difference between an upstream side and a downstream side of the throttle valve. Therefore, even if throttle bodies that have some differences in size or configurations have been used, the projections of the rubber seal members may closely contact the seat surfaces of the throttle bodies, so that air-tight seal can be maintained.
However, this sealing structure still has problems as will be hereinafter explained with reference to FIGS. 4 and 5, which show schematic sectional plan view and a cross sectional view taken along line V—V in FIG. 4, respectively, of a known variable flow control valve incorporating the teaching of the throttle valve of the above publication. Referring to FIGS. 4 and 5, resilient seal members 12 made of rubber are attached to a valve member 13 and oppose to seat surfaces formed on a wall of an air flow channel defined in a valve body 14. However, because clearances 15 may be formed between the valve 13 and the inner wall of the valve body 14 at both circumferential ends of each seal member 12, the air may flow through the clearances 15 via positions adjacent to the circumferential ends of the seal members 12, resulting in leakage of air. Therefore, air-tight seal may not be maintained.